“Navinder worked hard and traded diligently whilst at Futex,” UK-based Futex said in a statement. “There were no incidents of any impropriety during his time with Futex.”

Sarao was arrested in London this week on charges that he helped trigger a 1,000-point swing in the Dow during the May 6, 2010, crash by flooding the market with fake orders for stock market futures.

Sarao netted $40 million by manipulating the market through a practice known as “spoofing,” according to the US Justice Department, which is seeking his extradition to the US.

Sarao worked at Futex for five years until 2008, according to the company, which rents office space and computer systems to traders in return for a fee and a cut of their profits.

During that time, Sarao boasted that he was raking in $45,000 to $133,000 a day, according an e-mail in the Justice complaint.

“You must understand that for me to be in the top 30 is not a vanity thing,” he wrote in a 2007 e-mail to Magnus Greaves, founder of the now-defunct Doubledown Media, looking to be part of the company’s “30 under 30” list. “I prefer to keep a low profile and indeed hide my [profits and losses] from my trading colleagues.”